Regulation of protein longevity via the ubiquitin (Ub) - proteasome pathway is fundamental to eukaryotic biology. Ubiquitin E3 ligases (E3s) interact with substrate proteins and provide specificity to the pathway. A small subset of E3s bind to specific exposed N-termini (N-degrons) and promote the ubiquitination of the bound protein. Collectively these E3s, and other N-degron binding proteins, are known as N-recognins. There is considerable functional divergence between fungi, animal, and plant N-recognins. In plants, at least three proteins (PRT1, PRT6, and BIG) participate in the Arg/N-degron pathway. PRT1 has demonstrated E3 ligase activity, whereas PRT6 and BIG are candidate E3s. The Arg/N-degron pathway plays a central role in plant development, germination, and submersion tolerance. The pathway has been manipulated both to improve crop performance and for conditional protein degradation. A more detailed structural and biochemical understanding of the Arg/N-recognins and their substrates is required to fully realise the biotechnological potential of the pathway. This perspective focuses on the structural and molecular details of substrate recognition and ubiquitination in the plant Arg/N-degron pathway. While PRT1 appears to be plant specific, the PRT6 and BIG proteins are similar to UBR1 and UBR4, respectively. Analysis of the cryo-EM structures of Saccharomyces UBR1 suggests that the mode of ubiquitin conjugating enzyme (E2) and substrate recruitment is conserved in PRT6, but regulation of the two N-recognins may be significantly different. The structurally characterised domains from human UBR4 are also likely to be conserved in BIG, however, there are sizeable gaps in our understanding of both proteins.

中文翻译：

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植物 Arg/N-degron 通路中的泛素 E3 连接酶。


通过泛素 （Ub） - 蛋白酶体途径调节蛋白质寿命是真核生物学的基础。泛素 E3 连接酶 （E3） 与底物蛋白相互作用，并为通路提供特异性。一小部分 E3 与特异性暴露的 N 末端 （N-degrons） 结合并促进结合蛋白的泛素化。这些 E3 和其他 N-degron 结合蛋白统称为 N-识别蛋白。真菌、动物和植物 N 识别素之间存在相当大的功能差异。在植物中，至少三种蛋白质 （PRT1 、 PRT6 和 BIG） 参与 Arg/N-degron 途径。PRT1 已证明 E3 连接酶活性，而 PRT6 和 BIG 是候选 E3。Arg/N-degron 通路在植物发育、发芽和耐浸没性中起着核心作用。该途径已纵以改善作物性能和条件性蛋白质降解。需要对 Arg/N-识别素及其底物进行更详细的结构和生化理解，以充分实现该途径的生物技术潜力。该观点侧重于植物 Arg/N-degron 途径中底物识别和泛素化的结构和分子细节。虽然 PRT1 似乎是植物特异性的，但 PRT6 和 BIG 蛋白分别与 UBR1 和 UBR4 相似。对酵母菌 UBR1 的冷冻电镜结构的分析表明，泛素结合酶 （E2） 和底物募集的模式在 PRT6 中是保守的，但两种 N 识别素的调节可能显着不同。来自人类 UBR4 的结构域也可能在 BIG 中是保守的，但是，我们对这两种蛋白质的理解存在相当大的差距。